1. Field of the Invention
The present invention relates to a method of and an apparatus for cooling an electrostatic chuck of a semiconductor fabricating device. More particularly, the present invention relates to a method of and an apparatus for stabilizing the temperature of the electrostatic chuck.
2. Description of the Related Art
A semiconductor device comprises a great number of electric circuits. These circuits are formed on a wafer using a method known as photolithography. The photolithography method includes forming a conductive layer and an insulation layer on the wafer by vapor deposition, and then etching the conductive layer to pattern the conductive material and thereby form circuits.
The vapor deposition process and the etching process are performed in respective process chambers. An electrostatic chuck firmly fixes the wafer in the process chamber during the deposition or etching process. Recently, plasma deposition and etching apparatuses have widely used plasma for forming layers on a wafer and etching the layers, respectively.
In a typical plasma processing apparatus, the electrostatic chuck (hereinafter referred as ESC) is used as an electrode to form plasma from gas introduced into the chamber. Accordingly, when the plasma process is carried out, the temperature of the ESC temperature increases due to the hot plasma formed in the chamber. The temperature characteristics of the wafer supported by the electrostatic chuck are directly influenced by the temperature change of the ESC. Fluctuations in the thermal environment not only may cause the critical dimension (CD) of a wafer to vary from the desired CD, but also may cause the critical dimension to vary among the wafers that are sequentially processed in the apparatus.
The ESC is, therefore, usually cooled by a refrigeration unit mounted on the outside of the process chamber so as to minimize the thermal effect of the plasma on the wafer.
The conventional refrigeration unit circulates coolant from outside the process chamber to a heat exchanger disposed on the ESC inside the chamber. Accordingly, the ESC is cooled by a heat exchange process effected between the ESC and the coolant. The refrigeration unit withdraws the coolant from the ESC, cools the coolant and then again supplies the coolant (now cooled) to the ESC.
Refrigeration unit temperature sensors are installed on the outlet and on the inlet of the refrigeration unit, respectively, outside the process chamber. An outer temperature sensor is installed on a coolant-supplying pipe just outside the process chamber. The refrigeration system controls the temperature of the coolant in response to the temperatures detected by the refrigeration unit temperature sensors and the outer temperature sensor.
However, the conventional refrigeration system has a problem in that it can not accurately control the temperature of the coolant because it possesses an inherent delay in response time to changes in temperature of the ESC. This inherent delay in response time occurs because the coolant in the chamber takes time to reach the outer temperature sensor installed at the coolant-supplying pipe. Furthermore, significant time elapses before the coolant is re-supplied to the chamber, i.e., after it has been cooled in response to the detected temperatures. Therefore, the conventional refrigeration system makes it impossible to control the temperature of the electrostatic chuck in real time based on the temperature of the coolant.
Also, the coolant is supplied to the electrostatic chuck inside the chamber at a temperature independent of an intervening change in temperature of the electrostatic chuck. That is, again, the conventional refrigeration system does not offer a suitable response to actual changes in temperature of the electrostatic chuck. In addition, the conventional refrigeration system cannot prevent the ESC temperature from fluctuating widely due to a temperature difference between the ESC and the temperature to which a refrigerator of the system is set.
Therefore, an object of the present invention is to overcome the problems presented by the prior art.
Accordingly, a first object of the present invention is to provide a method of and an apparatus for regulating the temperature of an electrostatic chuck, wherein there occurs only a small difference between the temperature setting of the refrigerator and the ESC temperature, and wherein the time it takes to control the temperature of the coolant upon changes in temperature of the ESC is minimal, whereby the ESC temperature can be kept nearly constant.
A second object of the present invention is to provide a method of and an apparatus for regulating the temperature of an electrostatic chuck, characterized by high cooling efficiency and low cost (cost savings in connection with the coolant).
In a semiconductor fabricating apparatus according to the present invention, a refrigeration system for regulating the temperature of an electrostatic chuck comprises a heat exchanger for effecting a heat exchange between the electrostatic chuck and a coolant, a refrigerator disposed outside the process chamber for cooling down the coolant withdrawn from the heat exchanger and re-supplying the coolant to the heat exchanger, a temperature sensor disposed in the body of the electrostatic chuck itself for detecting an ESC temperature, and a temperature controller for controlling the refrigerator to cool the high temperature coolant withdrawn from the heat exchanger to a desired temperature in response to a temperature signal issued by the temperature sensor.
A coolant supplying pipe connects an inlet of the heat exchanger and an outlet of the refrigerator. A coolant withdrawal pipe connects an outlet of the heat exchanger and an inlet of the refrigerator. Thus, the heat exchanger, refrigerator and coolant pipes constitute a coolant loop through which the coolant circulates.
A deionizing filter may be provided in the coolant loop for deionizing the coolant withdrawn from the heat exchanger. In this case, the deionizing filter is disposed in-line with the coolant withdrawal pipe near the inlet of the refrigerator.
According to the present invention, the coolant is preferably a mixture of deionized water and an anti-freeze. And, the anti-freeze is preferably ethylene glycol. In this case, the ratio of the deionized water to the anti-freeze is 5:5.
In the method of regulating the temperature of the electrostatic chuck according to the present invention, the ESC temperature is measured directly from the body of the electrostatic chuck (by the temperature sensor installed in the body of the electrostatic chuck), coolant is supplied into the electrostatic chuck (via a coolant passageway of the heat exchanger) to chill the electrostatic chuck, and the coolant is chilled (by the refrigerator disposed outside the plasma chamber) in response to the detected ESC temperature.